Decoding barcodes displayed on cell phone

ABSTRACT

A method of decoding a barcode includes generating a first illumination towards a target object with a first illumination level, capturing a first image during a first exposure time period, and determining a first location and a second location on a scan line in the first image to find a switchover condition. If the switchover condition indicates the presence of a mobile display device, the method further includes generating a second illumination towards the target object with a second illumination level, capturing a second image during a second exposure time period, and decoding the barcode in the second image. Here, at least one of the second illumination level and the second exposure time period is determined based on values of pixels on the scan line between the first location and the second location.

RELATED APPLICATIONS

The present application is related to claims benefit under 35 U.S.C.§119(e) from U.S. Provisional Patent Application Ser. No. 61/586,808,filed Jan. 15, 2012, titled “AUTOMATIC MODE SWITCHING FOR BARCODESDISPLAYED ON CELL PHONE”, the entire contents of which beingincorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to imaging-based barcodescanners.

BACKGROUND

Various electro-optical systems have been developed for reading opticalindicia, such as barcodes. A barcode is a coded pattern of graphicalindicia comprised of a series of bars and spaces of varying widths. In abarcode, the bars and spaces have differing light reflectingcharacteristics. Some of the barcodes have a one-dimensional structurein which bars and spaces are spaced apart in one direction to form a rowof patterns. Examples of one-dimensional barcodes include UniformProduct Code (UPC), which is typically used in retail store sales. Someof the barcodes have a two-dimensional structure in which multiple rowsof bar and space patterns are vertically stacked to form a singlebarcode. Examples of two-dimensional barcodes include Code 49 andPDF417.

Systems that use one or more imaging sensors for reading and decodingbarcodes are typically referred to as imaging-based barcode readers,imaging scanners, or imaging readers. An imaging sensor generallyincludes a plurality of photosensitive elements or pixels aligned in oneor more arrays. Examples of imaging sensors include charged coupleddevices (CCD) or complementary metal oxide semiconductor (CMOS) imagingchips.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying figures, where like reference numerals refer toidentical or functionally similar elements throughout the separateviews, together with the detailed description below, are incorporated inand form part of the specification, and serve to further illustrateembodiments of concepts that include the claimed invention, and explainvarious principles and advantages of those embodiments.

FIG. 1 shows an imaging scanner in accordance with some embodiments.

FIG. 2 is a schematic of an imaging scanner in accordance with someembodiments.

FIG. 3A shows a barcode displayed on a cell phone is scanned by a linerimager with the barcode aligned with the field of view (FOV) of theliner imager.

FIG. 3B show a plot of pixel brightness profile across an image of theparts of the barcode and the cell phone within the FOV in the FIG. 3A.

FIG. 3C show a plot of pixel brightness profile across an image of theparts of the barcode and the cell phone within the FOV in the FIG. 3Aafter the exposure is adjusted is based on the center portion of thescan.

FIG. 4 is a flowchart of a method 100 of decoding a barcode inaccordance with some embodiments.

FIG. 5 is the histogram of the pixel brightness profile in FIG. 3B

Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale. For example, the dimensions of some of the elements inthe figures may be exaggerated relative to other elements to help toimprove understanding of embodiments of the present invention.

The apparatus and method components have been represented whereappropriate by conventional symbols in the drawings, showing only thosespecific details that are pertinent to understanding the embodiments ofthe present invention so as not to obscure the disclosure with detailsthat will be readily apparent to those of ordinary skill in the arthaving the benefit of the description herein.

DETAILED DESCRIPTION

FIG. 1 shows an imaging scanner 50 in accordance with some embodiments.The imaging scanner 50 has a window 56 and a housing 58 with a handle.The imaging scanner 50 also has a base 52 for supporting itself on acountertop. The imaging scanner 50 can be used in a hands-free mode as astationary workstation when it is placed on the countertop. The imagingscanner 50 can also be used in a handheld mode when it is picked up offthe countertop and held in an operator's hand. In the hands-free mode,products can be slid, swiped past, or presented to the window 56. In thehandheld mode, the imaging scanner 50 can be moved towards a barcode ona product, and a trigger 54 can be manually depressed to initiateimaging of the barcode. In some implementations, the base 52 can beomitted, and the housing 58 can also be in other shapes. In FIG. 1, acable is also connected to the base 52. In other implementations, whenthe cable connected to the base 52 is omitted, the imaging scanner 50can be powered by an on-board battery and it can communicate with aremote host by a wireless link.

FIG. 2 is a schematic of an imaging scanner 50 in accordance with someembodiments. The imaging scanner 50 in FIG. 2 includes the followingcomponents: (1) an imaging sensor 62 positioned behind an imaging lensarrangement 60; (2) an illuminating lens arrangement 70 positioned infront of an illumination source 72; (3) an aiming pattern generator 80positioned in front of an aiming light source 82; and (4) a controller90. In FIG. 2, the imaging lens arrangement 60, the illuminating lensarrangement 70, and the aiming pattern generator 80 are positionedbehind the window 56. The imaging sensor 62 is mounted on a printedcircuit board 91 in the imaging scanner.

The imaging sensor 62 can be a CCD or a CMOS imaging device. The imagingsensor 62 generally includes multiple pixel elements. These multiplepixel elements can be formed by a one-dimensional array ofphotosensitive elements arranged linearly in a single row. Thesemultiple pixel elements can also be formed by a two-dimensional array ofphotosensitive elements arranged in mutually orthogonal rows andcolumns. The imaging sensor 62 is operative to detect light captured byan imaging lens arrangement 60 along an optical path or axis 61 throughthe window 56. Generally, the imaging sensor 62 and the imaging lensarrangement 60 are designed to operate together for capturing lightscattered or reflected from a barcode 40 as pixel data over atwo-dimensional imaging field of view (FOV).

The barcode 40 generally can be located anywhere in a working range ofdistances between a close-in working distance (WD1) and a far-outworking distance (WD2). In one specific implementation, WD1 is in aclose proximity to the window 56, and WD2 is about a couple of feet fromthe window 56. Some of the imaging scanners can include a range findingsystem for measuring the distance between the barcode 40 and the imaginglens arrangement 60. Some of the imaging scanners can include anauto-focus system to enable a barcode be more clearly imaged with theimaging sensor 62 based on the measured distance of this barcode. Insome implementations of the auto-focus system, the focus length of theimaging lens arrangement 60 is adjusted based on the measured distanceof the barcode. In some other implementations of the auto-focus system,the distance between the imaging lens arrangement 60 and the imagingsensor 62 is adjusted based on the measured distance of the barcode.

In FIG. 2, the illuminating lens arrangement 70 and the illuminationsource 72 are designed to operate together for generating anilluminating light towards the barcode 40 during an illumination timeperiod. The illumination source 72 can include one or more lightemitting diodes (LED). The illumination source 72 can also include alaser or other kind of light sources. The aiming pattern generator 80and the aiming light source 82 are designed to operate together forgenerating a visible aiming light pattern towards the barcode 40. Suchaiming pattern can be used by the operator to accurately aim the imagingscanner at the barcode. The aiming light source 82 can include one ormore light emitting diodes (LED). The aiming light source 82 can alsoinclude a laser, LED, or other kind of light sources.

In FIG. 2, the controller 90, such as a microprocessor, is operativelyconnected to the imaging sensor 62, the illumination source 72, and theaiming light source 82 for controlling the operation of thesecomponents. The controller 90 can also be used to control other devicesin the imaging scanner. The imaging scanner 50 includes a memory 94 thatcan be accessible by the controller 90 for storing and retrieving data.In many embodiments, the controller 90 also includes a decoder fordecoding one or more barcodes that are within the imaging field of view(FOV) of the imaging scanner 50. In some implementations, the barcode 40can be decoded by digitally processing a captured image of the barcodewith a microprocessor.

In operation, in accordance with some embodiments, the controller 90sends a command signal to energize the illumination source 72 for apredetermined illumination time period. The controller 90 then exposesthe imaging sensor 62 to capture an image of the barcode 40. Thecaptured image of the barcode 40 is transferred to the controller 90 aspixel data. Such pixel data is digitally processed by the decoder in thecontroller 90 to decode the barcode. The information obtained fromdecoding the barcode 40 is then stored in the memory 94 or sent to otherdevices for further processing.

Imaging barcode readers generally have its own internal illuminationsystem to provide light to a barcode target. The light source isgenerally collinear with the imaging system for efficiency. This workswell on barcodes on printed media because reflected light is generallyscattered. Recent years the barcode industry has witnessed the rise ofindicia presented on electronic media such as cell phones. Generally,the barcode is presented on an LC or AMOLED display behind a glasswindow. Unfortunately specular reflection of the light source from theglass usually blinds the imagers and confuses exposure routine.Subsequently, the embedded illumination must be turned off and exposuretime increased to read such barcodes. The controller of the reader mayhave multiple exposure times: short to read paper barcodes and avoidhandjitter, and long exposure to read electronic barcodes when it isdimly lit. However, the disadvantage is that this usually requires aspecial mode and often results in less aggressive perceived scanningperformance. Moreover, since the illumination needs to be off duringlong exposure, the blinking of the LEDs becomes noticeable and is oftennot desirable or acceptable.

In linear imager, the problem with specular reflection can be mitigatedby tilting the cell phone at a substantial angle to the scanner.However, it was found that the display transmittance falls offexponentially as function of angle, which usually results in long pixelexposures. It was also found that the grinded edges of the glass windowsand shinny frames around the cell phone reflect incident light to alldirections that even at sufficiently large reading angle (pitch), twosymmetrical (could be asymmetrical depending on the yaw angle) bands oflight still appear on the captured image. These regions are typicallybrighter than the barcode displayed on a dimly lit cell phone.Therefore, this often confuses the auto exposure routine and results inno decode.

It is desirable to have an imaging scanner that utilizes specialfeatures on the cell phone to automatically enter a mode optimized forreading barcodes displayed on cell phones. Most modern cell phones usechemically strengthened glass as cover windows for the display. Theedges of the windows are typically chamfered and grinded for improveddurability and safety during handling. The frame or enclosuresurrounding the cover windows can be either shinny or dull. The grindededges and the frame (especially with normal wear and tear) on the cellphone can randomly scatter incident light that the reflections arepicked up by the sensor even at oblique pitch angles. These reflectionsemerge as bright or saturated bands on the captured image. They canconsist of different sizes depending on the distance of cell phone tothe scanner, or the size and surface finish of the grinded window edgesand the surrounding frames.

This presents a serious challenge to decode barcodes displayed on dimlylit cell phones. The contrast between the bright bands and the actualmobile barcode are so high that a typical automatic exposure routinewill completely ignore or miss the barcode of interest. FIG. 3A shows abarcode 40 displayed on a cell phone 45 is scanned by a liner imager,with the barcode 40 aligned with the field of view (FOV) of the linerimager. FIG. 3B show a plot of pixel brightness profile across an imageof the parts of the barcode 40 and the cell phone 45 within the FOV inthe FIG. 3A, with the corresponding horizontal axis aligned accordingly,when the display brightness of the cell phone 45 is set to a relativelylow level. In FIG. 3B, the pixel brightness profile shows two nearlysaturated bands 108 and 109 outside the quiet region 102 of the barcode.These bright regions can be either hand holding the mobile device,background or bright reflected surfaces as described earlier. The partbetween the bright regions can either be total dark or be so dim thatsometimes only part of the entire barcode is shown. As can be easilyseen on the plot in FIG. 3B, there is little or no modulation in theregion corresponding to the actual display area. It would be desirableto have an imagining scanner that has certain automatic exposure (AE)control for adjusting the amount of the exposure to achieve desiredsetting for at least for the part of the image that contains thebarcode. It would be desirable to have a method to detect the presenceof a mobile device and adjust the exposure accordingly so that themobile screen showing the barcode will get adequate exposure to ensuresuccessful decoding.

In this following, a method of decoding a barcode with an imagingscanner having automatic exposure (AE) control is described. The imagingscanner includes an imaging sensor having an array of photosensitiveelements. In general, the method of decoding a barcode within an imagingfield of view of imaging scanner includes the following: (1) generatinga first illumination towards a target object with a first illuminationlevel; (2) detecting light from the target object with the array ofphotosensitive elements in the imaging sensor while the target object isilluminated by the first illumination to capture a first image during afirst exposure time period; (3) determining a first location and asecond location on a scan line in the first image to find a switchovercondition. If the switchover condition indicates the presence of amobile display device in the first image, the above described methodfurther includes the following: (1) generating a second illuminationtowards the target object with a second illumination level, (2)detecting light from the target object with the array of photosensitiveelements in the imaging sensor while the target object is illuminated bythe second illumination to capture a second image during a secondexposure time period, and (3) decoding the barcode in the second image.Here, at least one of the second illumination level and the secondexposure time period is determined based on values of pixels on the scanline between the first location and the second location in the firstimage.

FIG. 4 is a flowchart of a method 100 of decoding a barcode inaccordance with some embodiments. As shown in FIG. 4, at block 110 andblock 120, a first illumination is generated towards the target object45 with a first illumination level, and a first image of the targetobject 45 is captured with first exposure time period while the targetobject is illuminated by the first illumination. Then, at block 130, afirst location and a second location on a scan line in the first imageis determined, and the switchover condition is evaluated at block 140 todetect the presence of mobile device. In some implementations, if theswitchover condition is not met, the first image is processed fordecoding a barcode. In some other implementations, if the switchovercondition is not met, the method 100 will restart from block 110.

In order to determine the switchover condition, the value of “bright”needs to be defined. This value is obtained from histogram of the scan.FIG. 5 is the histogram of the pixel brightness profile in FIG. 3B. Theindex of the maximum non-zero element of the histogram is the maximumpixel value of the scan. We define the value of “bright” to be a certainpercentage of the maximum brightness, say 75%. In some implementations,such threshold pixel value is set at a predetermined fraction of themaximum pixel value in the first image, and the predetermined fractioncan be chosen to be a number between 60% to 90%. Based on the assumptionthat the mobile device display is in the center, or near its proximity,of the scan line, the algorithm searches from the center of the scan tothe left and right and stops at the locations of which the value of thepixel reaches “bright”. The left and right locations are respectivelyused as the first location and the second location on the scan line forfinding the switchover condition. The distance between the left andright locations is the size of the mobile device display scaled by thelens magnification. If the size is large enough, say more than ¼ of thetotal scan, the algorithm determines that a mobile device is beenscanned. In other implementations, the algorithm determines that amobile device is been scanned, if the distance from the left location tothe right location as the percentage of the total length of the scanline is larger than a predetermined factor which can be chosen to be anumber between 20% to 80%.

As shown in FIG. 4, if the switchover condition is satisfied, then, atblock 150, an exposure level based on values of pixels on the scan linebetween the first location and the second location in the first image isdetermined That is, if it is determined that a mobile device is beenscanned, the automatic exposure (AE) control will adjust exposure basedon center portion of the scan. The result is a brighter portion coveringmobile device screen and very bright regions surrounding the center,which makes it possible to decode the barcodes on very dim displays. Forexample, as shown in FIG. 3C, after the exposure is adjusted is based onthe center portion of the scan, the region 102 corresponding to thebarcode will have significant brightness modulations in the pixelbrightness profile, despite that the brightness of the band 108 and band109—which are outside the region corresponding to the actual displayarea—can be so bright as to be off the scale. In FIG. 4, after the new(or second) exposure level is determined, at block 160 and block 170, asecond illumination is generated towards the target object with a secondillumination level, and a second image of the target object is capturedby the second exposure time period the while the target object isilluminated by the second illumination. Finally, at block 180, thebarcode in the second image is decoded.

The method described above can be applied to both the linear imager andthe area imager. The barcode on the cell phone can be 1-d barcode or 2-dbarcode. When above described method is applied to the linear imager,the scan line can be formed by one or more parallel 1-d arrays ofphotosensitive elements. When above described method is applied to thearea imager that includes a two-dimensional array of photosensitiveelements, and the scan line can be formed by a virtual scan line formedby pixels in the first image.

In the foregoing specification, specific embodiments have beendescribed. However, one of ordinary skill in the art appreciates thatvarious modifications and changes can be made without departing from thescope of the invention as set forth in the claims below. Accordingly,the specification and figures are to be regarded in an illustrativerather than a restrictive sense, and all such modifications are intendedto be included within the scope of present teachings.

The benefits, advantages, solutions to problems, and any element(s) thatmay cause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeatures or elements of any or all the claims. The invention is definedsolely by the appended claims including any amendments made during thependency of this application and all equivalents of those claims asissued.

Moreover in this document, relational terms such as first and second,top and bottom, and the like may be used solely to distinguish oneentity or action from another entity or action without necessarilyrequiring or implying any actual such relationship or order between suchentities or actions. The terms “comprises,” “comprising,” “has”,“having,” “includes”, “including,” “contains”, “containing” or any othervariation thereof, are intended to cover a non-exclusive inclusion, suchthat a process, method, article, or apparatus that comprises, has,includes, contains a list of elements does not include only thoseelements but may include other elements not expressly listed or inherentto such process, method, article, or apparatus. An element proceeded by“comprises . . . a”, “has . . . a”, “includes . . . a”, “contains . . .a” does not, without more constraints, preclude the existence ofadditional identical elements in the process, method, article, orapparatus that comprises, has, includes, contains the element. The terms“a” and “an” are defined as one or more unless explicitly statedotherwise herein. The terms “substantially”, “essentially”,“approximately”, “about” or any other version thereof, are defined asbeing close to as understood by one of ordinary skill in the art, and inone non-limiting embodiment the term is defined to be within 10%, inanother embodiment within 5%, in another embodiment within 1% and inanother embodiment within 0.5%. The term “coupled” as used herein isdefined as connected, although not necessarily directly and notnecessarily mechanically. A device or structure that is “configured” ina certain way is configured in at least that way, but may also beconfigured in ways that are not listed.

It will be appreciated that some embodiments may be comprised of one ormore generic or specialized processors (or “processing devices”) such asmicroprocessors, digital signal processors, customized processors andfield programmable gate arrays (FPGAs) and unique stored programinstructions (including both software and firmware) that control the oneor more processors to implement, in conjunction with certainnon-processor circuits, some, most, or all of the functions of themethod and/or apparatus described herein. Alternatively, some or allfunctions could be implemented by a state machine that has no storedprogram instructions, or in one or more application specific integratedcircuits (ASICs), in which each function or some combinations of certainof the functions are implemented as custom logic. Of course, acombination of the two approaches could be used.

Moreover, an embodiment can be implemented as a computer-readablestorage medium having computer readable code stored thereon forprogramming a computer (e.g., comprising a processor) to perform amethod as described and claimed herein. Examples of suchcomputer-readable storage mediums include, but are not limited to, ahard disk, a CD-ROM, an optical storage device, a magnetic storagedevice, a ROM (Read Only Memory), a PROM (Programmable Read OnlyMemory), an EPROM (Erasable Programmable Read Only Memory), an EEPROM(Electrically Erasable Programmable Read Only Memory) and a Flashmemory. Further, it is expected that one of ordinary skill,notwithstanding possibly significant effort and many design choicesmotivated by, for example, available time, current technology, andeconomic considerations, when guided by the concepts and principlesdisclosed herein will be readily capable of generating such softwareinstructions and programs and ICs with minimal experimentation.

The Abstract of the Disclosure is provided to allow the reader toquickly ascertain the nature of the technical disclosure. It issubmitted with the understanding that it will not be used to interpretor limit the scope or meaning of the claims. In addition, in theforegoing Detailed Description, it can be seen that various features aregrouped together in various embodiments for the purpose of streamliningthe disclosure. This method of disclosure is not to be interpreted asreflecting an intention that the claimed embodiments require morefeatures than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive subject matter lies in less than allfeatures of a single disclosed embodiment. Thus the following claims arehereby incorporated into the Detailed Description, with each claimstanding on its own as a separately claimed subject matter.

What is claimed is:
 1. A method of decoding a barcode within an imagingfield of view of an imaging system that includes an imaging sensorhaving an array of photosensitive elements, the method comprising:generating a first illumination towards a target object with a firstillumination level; detecting light from the target object with thearray of photosensitive elements in the imaging sensor while the targetobject is illuminated by the first illumination to capture a first imageduring a first exposure time period; determining a first location and asecond location on a scan line in the first image to find a switchovercondition; if the switchover condition indicates the presence of amobile display device in the first image, (1) generating a secondillumination towards the target object with a second illumination level,and (2) detecting light from the target object with the array ofphotosensitive elements in the imaging sensor while the target object isilluminated by the second illumination to capture a second image duringa second exposure time period; wherein at least one of the secondillumination level and the second exposure time period is determinedbased on values of pixels on the scan line between the first locationand the second location in the first image; and finding a selecteddistance between the first location and the second location on the scanline; and wherein the switchover condition indicates the presence of amobile display device in the first image if the ratio between theselected distance and the total length of the scan line in the firstimage is larger than a predetermined factor.
 2. The method of claim 1,wherein the predetermined factor is chosen to be between 20% to 80%. 3.The method of claim 1, wherein the predetermined factor is chosen to be25%.
 4. The method of claim 1, wherein said determining comprisesdetermining a threshold pixel value for finding the first location andthe second location on the scan line.
 5. The method of claim 1, whereinsaid determining comprises determining a threshold pixel value forfinding the first location and the second location on the scan line,wherein the threshold pixel value is determined from a histogram of thefirst image.
 6. The method of claim 1, wherein the array ofphotosensitive elements forms the scan line of a linear imaging device.7. A method of decoding a barcode within an imaging field of view of animaging system that includes an imaging sensor having an array ofphotosensitive elements, the method comprising: generating a firstillumination towards a target object with a first illumination level;detecting light from the target object with the array of photosensitiveelements in the imaging sensor while the target object is illuminated bythe first illumination to capture a first image during a first exposuretime period; determining a first location and a second location on ascan line in the first image to find a switchover condition; if theswitchover condition indicates the presence of a mobile display devicein the first image, (1) generating a second illumination towards thetarget object with a second illumination level, and (2) detecting lightfrom the target object with the array of photosensitive elements in theimaging sensor while the target object is illuminated by the secondillumination to capture a second image during a second exposure timeperiod; wherein at least one of the second illumination level and thesecond exposure time period is determined based on values of pixels onthe scan line between the first location and the second location in thefirst image; determining a threshold pixel value for finding the firstlocation and the second location on the scan line, wherein the thresholdpixel value is set at a predetermined fraction of the maximum pixelvalue in the first image; and wherein the predetermined fraction ischosen to be between 60% to 90%.
 8. The method of claim 7, wherein thepredetermined fraction is chosen to be 75%.
 9. A method of decoding abarcode within an imaging field of view of an imaging system thatincludes an imaging sensor having an array of photosensitive elementsthe method comprising: generating a first illumination towards a targetobject with a first illumination level; detecting light from the targetobject with the array of photosensitive elements in the imaging sensorwhile the target object is illuminated by the first illumination tocapture a first image during a first exposure time period; determining afirst location and a second location on a scan line in the first imageto find a switchover condition; if the switchover condition indicatesthe presence of a mobile display device in the first image, (3)generating a second illumination towards the target object with a secondillumination level, and (4) detecting light from the target object withthe array of photosensitive elements in the imaging sensor while thetarget object is illuminated by the second illumination to capture asecond image during a second exposure time period; wherein at least oneof the second illumination level and the second exposure time period isdetermined based on values of pixels on the scan line between the firstlocation and the second location in the first image; and wherein thearray of photosensitive elements is a two-dimensional array ofphotosensitive elements, and wherein the scan line is a virtual scanline formed by pixels in the first image.
 10. A method of decoding abarcode within an imaging field of view of an imaging system thatincludes an imaging sensor having an array of photosensitive elements,the method comprising: generating a first illumination towards a targetobject with a first illumination level; detecting light from the targetobject with the array of photosensitive elements in the imaging sensorwhile the target object is illuminated by the first illumination tocapture a first image during a first exposure time period; determining afirst location and a second location on a scan line in the first imageto find a switchover condition; if the switchover condition indicatesthe presence of a mobile display device in the first image, (1)generating a second illumination towards the target object with a secondillumination level, and (2) detecting light from the target object withthe array of photosensitive elements in the imaging sensor while thetarget object is illuminated by the second illumination to capture asecond image during a second exposure time period; wherein at least oneof the second illumination level and the second exposure time period isdetermined based on values of pixels on the scan line between the firstlocation and the second location in the first image; and wherein theimaging sensor has a gain associated therewith, and wherein at least oneof the second illumination level, the second exposure time period, andthe gain of the imaging sensor is determined based on pixels on the scanline between the first location and the second location in the firstimage.
 11. An apparatus comprising: an imaging lens arrangement; animaging sensor including an array of photosensitive elements configuredto operate together with the imaging lens arrangement for detectinglight from a target object within an imaging field of view; anillumination source for generating an illumination; a controllerconfigured for generating a first illumination towards the target objectwith a first illumination level, detecting light from the target objectwith the array of photosensitive elements in the imaging sensor whilethe target object is illuminated by the first illumination to capture afirst image during a first exposure time period, determining a firstlocation and a second location on a scan line in the first image to finda switchover condition, and finding a selected distance between thefirst location and the second location on the scan line; wherein theswitchover condition indicates the presence of a mobile display devicein the first image if the ratio between the selected distance and thetotal length of the scan line in the first image is larger than apredetermined factor; wherein the controller is further configured for,in the event that the switchover condition indicates the presence of amobile display device in the first image, generating a secondillumination towards the target object with a second illumination level,and detecting light from the target object with the array ofphotosensitive elements in the imaging sensor while the target object isilluminated by the second illumination to capture a second image duringa second exposure time period; and wherein at least one of the secondillumination level and the second exposure time period is determinedbased on values of pixels on the scan line between the first locationand the second location in the first image.
 12. The apparatus of claim11, wherein the controller configured for decoding a barcode in thesecond image.
 13. The apparatus of claim 11, wherein the array ofphotosensitive elements forms the scan line of a linear imaging device.14. An apparatus comprising: an imaging lens arrangement; an imagingsensor including an array of photosensitive elements configured tooperate together with the imaging lens arrangement from a target objectwithin an imaging field of view; an illumination source for generatingan illumination; a controller configured for generating a firstillumination towards the target object with a first illumination level,detecting light from the target object with the array of photosensitiveelements in the imaging sensor while the target object is illuminated bythe first illumination to capture a first image during a first exposuretime period, and determining a first location and a second location on ascan line in the first image to find a switchover condition; wherein thecontroller is further configured for, in the event that the switchovercondition indicates the presence of a mobile display device in the firstimage, generating a second illumination towards the target object with asecond illumination level, and detecting light from the target objectwith the array of photosensitive elements in the imaging sensor whilethe target object is illuminated by the second illumination to capture asecond image during a second exposure time period; wherein at least oneof the second illumination level and the second exposure time period isdetermined based on values of pixels on the scan line between the firstlocation and the second location in the first image; and wherein thearray of photosensitive elements is a two-dimensional array ofphotosensitive elements, and wherein the scan line is a virtual scanline formed by pixels in the first image.
 15. An apparatus comprising:an imaging lens arrangement; an imaging sensor including an array ofphotosensitive elements configured to operate together with the imaginglens arrangement from a target object within an imaging field of view;an illumination source for generating an illumination; a controllerconfigured for generating a first illumination towards the target objectwith a first illumination level, detecting light from the target objectwith the array of photosensitive elements in the imaging sensor whilethe target object is illuminated by the first illumination to capture afirst image during a first exposure time period, and determining a firstlocation and a second location on a scan line in the first image to finda switchover condition; wherein the controller is further configuredfor, in the event that the switchover condition indicates the presenceof a mobile display device in the first image, generating a secondillumination towards the target object with a second illumination level,and detecting light from the target object with the array ofphotosensitive elements in the imaging sensor while the target object isilluminated by the second illumination to capture a second image duringa second exposure time period; wherein at least one of the secondillumination level and the second exposure time period is determinedbased on values of pixels on the scan line between the first locationand the second location in the first image; and wherein the imagingsensor has a gain associated therewith, and wherein at least one of thesecond illumination level, the second exposure time period, and the gainof the imaging sensor is determined based on values of pixels on thescan line between the first location and the second location in thefirst image.
 16. A method of decoding a barcode within an imaging fieldof view of an imaging system that includes an imaging sensor having anarray of photosensitive elements, the method comprising: generating afirst illumination towards a target object with a first illuminationlevel; detecting light from the target object with the array ofphotosensitive elements in the imaging sensor while the target object isilluminated by the first illumination to capture a first image during afirst exposure time period; determining a first location and a secondlocation on a scan line in the first image to find a switchovercondition; if the switchover condition indicates the presence of amobile display device in the first image, (1) generating a secondillumination towards the target object with a second illumination level,(2) detecting light from the target object with the array ofphotosensitive elements in the imaging sensor while the target object isilluminated by the second illumination to capture a second image duringa second exposure time period, and wherein at least one of the secondillumination level and the second exposure time period is determinedbased on values of pixels on the scan line between the first locationand the second location in the first image, and (3) decoding the barcodein the second image; and wherein the array of photosensitive elements isa two-dimensional array of photosensitive elements, and wherein the scanline is a virtual scan line formed by pixels in the first image.
 17. Themethod of claim 16, wherein the array of photosensitive elements formsthe scan line of a linear imaging device.